Monday, June 6, 2011


This year's bicycle tour with some of my former classmates took me to the banks of the Main and Tauber rivers. One of the highlights on our trip was the city of Würzburg particularly known for its Residence Castle (UN heritage) and its two old hospitals Julius- and Bürgerspital where nowadays Fraconian wine is served in special bocksbeutel bottles.

Röntgen's  manuscript
Würzburg is also the city where in 1895 Wilhelm Conrad Röntgen discovered the roentgen rays better known in the US as x-rays. Röntgen modestly used to call them X-Strahlen in German or in the scientific language of the 19th century rayons x. The laboratory room where Röntgen made his discovery can in principle be visited but going there with two friends I found the door locked. Luckily enough an excellent booklet about the history of the new kind of radiation (Über eine neue Art von Strahlen) was on sale at the secretariat of the now material research institute for a ridiculous price of € 2.50.

Here I used the occasion to convince the two ladies present that I should be privileged to show to my two buddies Röntgen's lab since I had written way back in 1960 my diploma thesis about: Applying the contrast transfer function to x-ray picturing. Oh miracle, one of the girls left and came back with the key. The room we visited was filled with Ruhmkorff induction coils and Crookes tubes or Hittorf vacuum glass vessels. The picture below may give you an impression.

The room where Wilhelm Conrad Röntgen made his discovery
Röntgen was lucky that the vacuum he could achieve in his time was rather poor so when he applied high tension between two electrodes melted into a glass vessel the remaining positively charged gas ions hitting the metal cathode generated free electrons. These electrons in turn are accelerated by the high tension towards the anode producing x-ray bremsstrahlung. This term like eigenvalue is one of the few remaining German words or half-words in today's scientific language.

By the way, applying the contrast transfer function to the picture taken by Röntgen of a hand would have improved the quality of the photo considerably. Please compare the left hand on the left to the left hand on the right.

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